1. Field of the Invention
The present invention relates to a multi-channel optical connector and, more particularly, to a rugged-type multi-channel optical connector for use with optical transmitter modules and optical receiver modules.
2. Description of the Related Art
Recently, communication systems designers are vigorously adapting their designs for the use of optical fiber technology in various communication fields. Optical communication systems enable use of high frequency signals and suffer less signal loss than conductor based technologies and are therefore better suited for the high bandwidth communications that are increasingly in demand. Optical communication systems are suitable to use in high speed-long distance transmission systems.
During optical transmission of data, one channel of serial data is generally utilized for transmitting parallel data on N channels. In this case, the transmission speed of the serial data should be at least N times faster than each of the parallel data channels. High speed transmission circuits require expensive equipment; therefore, multiple transmission channels are often utilized to reduce the burden of a high speed transmitting circuit. In order to use multiple optical channels, a plurality of optical transmission systems, each including a light source, an optical fiber, and light detector, are required. For multi-channel optical transmitter/receiver modules, an accurate alignment of optical fibers with sources and detector is required not only for each channel but also for adjacent channels. Therefore, multi-channel optical transmitter/receiver modules need an optical connector which is highly accurate and, consequently, is more complicated than that of a single channel optical transmitter/receiver module.
FIG. 1 is an exemplary schematic diagram illustrating an active alignment method for a multi channel optical connector 101 and laser diodes 100. In order to arrange laser diodes 100, for example, with respect to optical fibers 110, laser diodes 100 are first fixed so that they are separated by regular, usually uniform, intervals. Next, optical fibers 110 are fixed on a block 120 having grooves with the same regular intervals with which the laser diodes have been fixed. Then, laser diodes 100 and optical fibers 110 are aligned by moving block 120 with respect to laser diodes 100. Block 120 can be moveable in all three directions. An optimal alignment between optical fibers 110 and laser diodes 100 can be achieved by monitoring the optical output power from each optical fiber of optical fibers 110 while moving block 120. When the output power from each of the optical fibers 110 is maximized, block 120 can be fixed relative to diodes 100. This method is referred to as the active alignment method because the maximum output power is sought by monitoring the optical output power from fibers 110. The active alignment method can approach the optimum arrangement, however it requires expensive equipment and a lot of labor hours to accomplish. Further, the active alignment method does not lend itself to systems where plugable connectors are desirable.
FIG. 2 is an exemplary schematic diagram illustrating a passive alignment method for a multi channel optical connector 201 and optical devices 200. In contrast to the active alignment method illustrated in FIG. 1, the passive alignment method does not include monitoring optical output power. Multi channel optical connector 201 includes an optical device array block 210 with optical devices 200, each electrically coupled to one of electrical conductors 211, arranged to have regular, uniform, intervals. Multi channel optical connector 201 also includes a multi channel optical fiber block 220 having optical fibers 221 arranged with the same regular intervals as that of optical devices 200 of optical device array block 210. Optical device array block 210 can be fixed on a substrate (not shown) by soldering. Multi channel optical fiber block 220 can be plugable. Optical fibers 221 are then aligned with optical devices 200 when multi channel optical fiber block 220 is plugged into optical device array block 210. Optical devices 200 can be laser diodes or photodiodes. Even though the passive alignment method is not optimized as with the active alignment method, it has the advantage of being faster (requiring fewer labor hours), requires less expensive equipment, and therefore is less expensive to perform.
FIG. 3 illustrates a conventional method of assembling connector 201 of FIG. 2. Typically, an optical transmitter/receiver module will include two connectors such as connector 201 of FIG. 2, arranged such that light sources in one module are coupled with light detectors in the other module via optical fibers. Optical fibers 320 are inserted in grooves 311 on a connector block 310. Optical fibers 320 can be multi mode or single mode optical fibers. Grooves 311 guide optical fibers 320 into holes 322, typical 250 xcexcm diameter holes, in connector block 310. Grooves 311 have uniform intervals between any two adjacent grooves 311. Optical fibers 320 are fixed in place by a cover 300, which can also be grooved with grooves 312 having the same uniform intervals as connector block 310. Connector block 310 is usually made from a plastic material for ease of manufacturing and lowered cost. End facets 321 of optical fibers 320 are usually smoothly polished in order to facilitate the coupling of light into and out of optical fibers 320.
TABLE 1 shows the result of a calculation for an allowable tolerance of the alignment depending on the various diameters of optical fibers and a coupling efficiency between the optical fiber and the optical devices. The calculations in TABLE 1 are based on several parameters. The allowable tolerance for alignment between a laser diode and an optical fiber is based on the requirement that more than about 90% of the maximum optical output of the laser diode be coupled into the optical fiber. The allowable tolerance of alignment between an optical fiber and a photo diode is based on the requirement that more than about 90% of the maximum light output from the optical fiber be coupled into the photo diode. The divergence angle of the laser diode beam is assumed to be about 15xc2x0. The diameter of the light receiving aperture of the photodiode is assumed to be about 200 xcexcm. Additionally, the laser diode is separated by about 450 xcexcm from the optical fiber.
If a 0.5 mm core diameter plastic optical fiber is used, it would be possible to manufacture a connector having approximately 100 xcexcm of allowable tolerance of alignment between the optical fiber and the laser diode by plastic molding. However, only 21% of the light output from the optical fiber can be coupled into the photodiode. Alternatively, if a 0.25 mm core diameter plastic optical fiber is used, 67% of the light output from the optical fiber can be coupled to the photodiode. The decreased diameter of the optical fiber can bring three times the signal to the photo diode without increasing the output of the laser diode; however, the allowable tolerance of alignment between the optical fiber and the laser diode would be reduced by an amount 0.29 that of the 0.5 mm diameter plastic optical fiber. It is very difficult to manufacture such a connector and satisfy the allowable tolerances with plastic molding. The passive alignment method is generally accomplished with plastic optical fiber having relatively large diameters, generally about 0.51xcx9c1.0 mm, for proper transmission of the optical signal.
If a 0.0625 mm diameter multi mode silica optical fiber is used, it is extremely difficult to satisfactorily manufacture the connector with the required reduced alignment tolerances by plastic molding. However, even though the amount of the output of the laser diode actually coupled into the multi mode silica optical fiber is small, all of the light coming out from the optical fiber can be coupled into the photodiode. Thus, the maximum output of the photodiode is almost the same as that of the 0.5 mm diameter optical fiber. The silica optical fiber is essential, however, for high speed-long distance signal transmission because silica optical fiber has almost no loss of power and a high cut-off frequency compared with plastic optical fiber. One drawback of using multi mode silica fiber is the small allowable tolerance in the alignment of fiber core with the laser diode. If the tolerance is exceeded the coupling efficiency will decrease, thereby increasing the loss in signal power.
FIG. 3A shows a typical optical fiber prepared for insertion into grooves 311 of connector block 310 (FIG. 3). Optical fiber 320 is a buffered optical fiber having a buffer 340. Buffer 340, for example, can be a 900 xcexcm diameter buffer. Buffer 340 is stripped away to expose buffer 341. Buffer 341, for example, can be a 250 xcexcm diameter buffer. Buffer 341 is inserted into one of holes 322 in connector block 310 and is guided by grooves 311. The center of buffer 341, however, may not be aligned with the center of fiber core 343, even though holes 321 have uniform intervals. Therefore, the centers of fiber core 343 may be arranged with non-uniform intervals.
However, the center of fiber core 343 is well aligned with the center of bare fiber 342, which may be a 125 xcexcm diameter fiber. If bare fiber 342 were placed into grooves 311 instead of buffer 341, the center of core 343 can be aligned accurately. However, it is difficult to make small diameter holes and grooves (125 xcexcm diameters, for example) using plastic injection molding since a very small and long needle-shaped molding core, which can be easily broken, is needed. Additionally, since the small diameter buffer 341 is fixed in connector block 310 while the large diameter buffer 340 is not, stress is induced at the junction between buffer 340 and buffer 341.
FIG. 3B shows a conventional assembly of a plurality of buffered fibers 330, which can be 900 xcexcm buffered fibers, and a conventional connector 332. Buffered fibers 330 are not enclosed in a cable sheath, and therefore are susceptible to breakage or excessive bending that can result in increased loss of power for the optical signal. Connector 332 mates with device module 334 thereby aligning the optical fibers 330 with light sources or light detectors present in the device module 334. Conventional connector 332 does not provide any strain relief mechanism, therefore any movement of connector 332 or even fibers 330 can potentially degrade the signal transmission characteristics at the interface of optical fibers 330 and the light source or the detector.
Therefore, there is need for a multi-channel optical connector capable of being precisely aligned in a fast, cost sensitive fashion to yield low loss connections especially for multimode fiber with 62.5 or 50 xcexcm diameter. It is also desirable to use rugged cable to avoid the breakage of fibers or the excessive bending of fibers resulting in higher loss of power for the optical signal. It is also desirable to provide a strain relief to avoid variation in transmission characteristics due to forces acting on the fibers or the connector body.
In accordance with the present invention, a multi-channel optical connector is disclosed that enables accurate alignment of optical fibers and optical devices, can have a rugged connector design that includes strain relief, and at the same time can support transmission of high frequency signals without interference or noise.
In one embodiment, the multi-channel optical connector includes a V-groove block, which can be made from silicon or plastic, and large holes for receiving at least one optical fiber so that at least one optical fiber is optically coupled to at least one optical device of a device array block. The multi channel optical connector is incorporated in a plastic molding that is complimentary in shape to the device array block, and thus can be plugged into the device array block.
In some embodiments, close tolerances are maintained in manufacturing of the multi-channel optical connector and the device array block, which results in accurate alignment of the fibers captured in the multi-channel optical connector with the optical devices in the device array block. The close tolerances can be achieved by using MEMS (Micro Electro Mechanical System) processing techniques. The bare fiber can be placed on V-grooves in the V-groove block.
The V-groove block can be made from silicon or plastic and is integrally fixed in the multi-channel optical fiber block. A buffered fiber is affixed in the multi-channel optical fiber block through holes in the multi-channel optical fiber block. The multi-channel optical fiber block also includes a trench structure between the holes and the V-grooves of the V-block so that bare fiber (e.g., 125 xcexcm diameter) can be placed in the V-grooves while a large diameter buffer (e.g., 900 xcexcm) is placed through the holes while reducing the stress between the buffered and unbuffered portions of the optical fibers.
The connector can also include a stopper and a housing. The stopper is fixedly attached to the sheath of a cable from which at least one of the optical fiber captured in the connector core is derived. The stopper is captured in the housing when the connector is plugged into the device module. The capturing of the stopper in the housing prevents the cable from translating or rotating and provides strain relief for the at least one optical fiber. Cable holding buttons in their locked position aid the stopper in preventing motion of the cable.
The connector is suitable for use with a cable that has a jacket enclosing buffered fibers. The buffer can be captured in the multi-channel optical connector; thus, bare fiber is not exposed to the elements, enhancing the structural ruggedness of the conductor. Additionally the housing surrounds the multi-channel optical connector and the jacketed fiber that is outside the buffer providing further protection and strain relief.
These and other embodiments of the invention are further discussed below with reference to the following figures.